But when using Get-WMIObject always run into
"rpc server is unavailable" in one direction and "Access denied" in the other direction.
Searched the forum but didnt find infos.
Switched off Firewalls: Still the same.
So I'm stuck.

Answers

1) Check that DCOM is enabled on both the host and the target PC. Check the following registry value on both computers:
Key: HKLM\Software\Microsoft\OLE, value: EnableDCOM, should be set to 'Y'

2) On a Windows XP Pro computer, make sure that remote logons are not being coerced to the GUEST account (aka "ForceGuest", which is enabled by default computers that are not attached to a domain). To do this, open the Local Security Policy editor (e.g. by
typing 'secpol.msc' into the Run box, without quotes). Expand the "Local Policies" node and select "Security Options". Now scroll down to the setting titled "Network access: Sharing and security model for local accounts". If this is set to "Guest only", change
it to "Classic" and restart your computer.

3) Make sure that no remote access or WMI-related services have been disabled. On an XP machine, the following services should be running (or at least allowed to start on demand):

This might help, but there's basically 2 kinds of remoting in your case, there's the Invoke-Command remoting which uses the WS-MAN protocol and there's WMI remoting which uses WMI (RPC over TCP). They are not really the same.

When you're doing this: Invoke-Command {Get-WmiObject ...} -ComputerName ... You are actually using WS-MAN to connect to the remote machine then the WMI call is being run locally.

The WMI remoting version generates always "access denied".
Firewalls are not the problem since I switched them temporary off.
I have no clue how to fix this. I'm looking for hints here.
And the question:
The GPO TrustedHosts setting and the Powershell TrustedHosts setting are storing the values not in the same place.
If I do it in the GPO it does not work. It works only when set in Powershell. So what is the difference?

The Windows Firewall on the target computer may block this kind of Remote access, and the account which is executing the command should exist also on the remote system and have Administrator permissions.

Between: Disabling ZoneAlarm may not be enough, I have seen cases, in which it had to be uninstalled to block no longer wanted communications.

1) Check that DCOM is enabled on both the host and the target PC. Check the following registry value on both computers:
Key: HKLM\Software\Microsoft\OLE, value: EnableDCOM, should be set to 'Y'

2) On a Windows XP Pro computer, make sure that remote logons are not being coerced to the GUEST account (aka "ForceGuest", which is enabled by default computers that are not attached to a domain). To do this, open the Local Security Policy editor (e.g. by
typing 'secpol.msc' into the Run box, without quotes). Expand the "Local Policies" node and select "Security Options". Now scroll down to the setting titled "Network access: Sharing and security model for local accounts". If this is set to "Guest only", change
it to "Classic" and restart your computer.

3) Make sure that no remote access or WMI-related services have been disabled. On an XP machine, the following services should be running (or at least allowed to start on demand):

The firewall may block the WMI and DCOM should be activated for the data client access. WMI uses Microsoft's Distributed Component Object Model (DCOM) to connect to and manage systems. You might have to configure some systemsto allow DCOM connections. Firewall
settings and locked-down DCOM permissions can block WMI's ability to remotely manage systems.

To enable WMI remotely, you must have local administrator rights on the remote computer. If you do not, access to that computer will be denied.
Please take joe's step to enable DCOM and check permissions.

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All users (including non-administrators) are able to query/read WMI data on the local computer.

For reading WMI data on a remote server, a connection needs to be made from your management computer (where our monitoring software is installed) to the server that you're monitoring (the target server). If the target server is running Windows Firewall (aka
Internet Connection Firewall) like what is shipped with Windows XP and Windows 2003, then you need to tell it to let remote WMI requests through<sup style="margin:0px;padding:0px;list-style:none;">2</sup>. This can only be done at the
command prompt. Run the following on the target computer if it is running a Windows firewall:

Open the Group Policy Object Editor snap-in to edit the Group Policy object (GPO) that is used to manage Windows Firewall settings in your organization.

Open Computer Configuration, open Administrative Templates, open Network, open Network Connections, open Windows
Firewall, and then open either Domain Profile or Standard Profile, depending on which profile you want to configure.

Oddly enough, every time I tried to run my remote PS script against one of my servers, I was getting a 1097 Usernv error in the App EV. Correcting time settings fixed this issue for me. This was on a 2003 box, fwiw